Method of applying a backing to a carpet and product

ABSTRACT

A CARPET IS FORMED BY ADHERING A SECONDARY BACKING TO A PRIMARY BACKING WITH A THIXOTROPIC POLYURETHANE COMPOSITION SO THAT THERE IS SUBSTANTIALLY COMPLETE SATURATION OF THE BUNDLE WRAP WITH THE COMPOSITION WITHOUT PERNETRATION THROUGH THE PRIMARY BACKING. THE COMPOSITION CONTAINS WATER, A POLYOL WITH A HYDROXYL NUMBER LESS THAN 100, A DIISOCYANATE, A FILLER AND A CATALYST AND HAS AN INITIAL VISCOSITY OF BETWEEN 30,000 AND 1008000 CPS. #7 SPINDLE BROOKFIELD RVF, A POT LIFE OF BETWEEN 10 AND 60 SECONDS AND IS EXPANDABLE BETWEEN 100 AND 400 WHEN COMPLETELY REACTED. IT IS APPLIED TO THE UNDERSIDE OF THE PRIMARY BACKING WITH A DOCTOR KNIFE AND HEATED. A SECONDARY BACKING IS APPLIED TO THE UNCURED COMPOSITION AFTER IT IS SPREAD ON THE PRIMARY BACKING AND THE RESULTANT LAMINATE IS SUBJECTED TO PRESSURE PRIOR TO CURING TO DISINTEGRATE SUBSTANTIALLY ALL OF THE CELLS IN THE POLYURETHANE.

C. E. TERRY Oct. 24, 1972 METHOD OF APPLYING A BACKING TO A CARPET ANDPRODUCT Filed Feb. 3, 1971 PMQWZU H MP3 H 5 INVENTOR CLAUDE E. TERRY BYW wi'aaa/ ATTORNEYS United States Patent 3,700,515 METHOD OF APPLYING ABACKING TO A CARPET AND PRODUCT Claude Edward Terry, Rockmart, Ga.,assignor to Textile Rubber & Chemical Company, Dalton, Ga. Filed Feb. 2,1971, Ser. No. 111,860 Int. Cl. D05c /00 US. Cl. 156-72 4 ClaimsABSTRACT OF THE DISCLOSURE A carpet is formed by adhering a secondarybacking to a primary backing with a thixotropic polyurethane compositionso' that there is substantially complete saturation of the bundle wrapwith the composition without penetration through the primary backing.The composition contains water, a polyol with a hydroxyl number lessthan 100, a diisocyanate, a filler and a catalyst and has an initialviscosity of between 30,000 and 100,000 cps. #7 spindle Brookfield RVF,a pot life of between 10 and 60 seconds and is expandable between 100and 400 when completely reacted. It is applied to the underside of theprimary backing with a doctor knife and heated. A secondary backing isapplied to the uncured composition after it is spread on the primarybacking and the resultant laminate is subjected to pressure prior tocuring to disintegrate substantially all of the cells in thepolyurethane.

This invention relates to a method for increasing the tuft lock ofcarpets and to the product obtained therefrom.

Presently, the large majority of the worlds carpets are produced by atufting process whereby yarn is stitched to a primary backing so that aportion of the yarn, known as the bundle wrap, protrudes through theprimary backing. After the stitching step, a secondary backing,generally jute, is adhesively applied to the primary backing and thebundle warp to provide dimensional stability, drape and enhance the tuftlock of the yarn, i.e., the strength with which the yarn is retained bythe primary backing. The adhesive used to laminate the secondary backingto the bundle wrap and primary backing is of major importance to thequality and performance of the carpet. It retains the yarn in place,secures the individual fibers of the yarn, prevents pilling of the yarn,controls dimensional stability (handle or drape) and retains thesecondary backing securely to the carpet. Also, it is extremelyimportant that the adhesive not migrate past the primary backing intothe exposed yarns otherwise the yarns will become stiff and the finalcarpet will be unacceptable.

Presently, the most widely used adhesive system is based upon a latex ora carboxylated latex that is applied to the underside of the primarybacking. The water in the latex system migrates through the primarybacking into the exposed yarns but the adhesive is retained by theprimary backing and the bundle wrap. The latex then is cured and thefinal carpet dried in large ovens at elevated temperatures. This is acostly process due to the large expense of the ovens, energyrequirements, floor space requirements, and labor to operate the ovens.A second adhesive system known as the hot-melt system based on the useof vinyl resins also is undesirable since it requires the expense ofspecially heated containers for transporting, storing, handling andapplying the resin to the under surface of the primary backing. Inaddition, these melted resins tend to migrate into the exposed yarnthereby producing unsatisfactory carpets.

The tuft lock of the carpets produced with either latex ice adhesives orthe hot-melt vinyl adhesives is undesirably low and the yarn can bepulled easilly from the primary backing. This low tuft lock hasnecessitated laying carpets in one or a few large pieces that conform tothe shape of the surface being covered rather than permitting the use ofsmall rectangular pieces to cover the same area since the risk ofpulling the yarn from the backing when using small pieces would beincreased substantially. If carpets having desirable handle and drapewere to have a tuft lock greater than presently available they could belaid in small rectangular pieces thus reducing installation labor costsgreatly.

It has been proposed to employ stronger adhesives between the layers toincrease tuft lock. However, adherence of a secondary backing to thebundle wrap of the carpet presents unique problems that have preventedthe use of these stronger adhesives. In order for the adhesive to befully effective in adhering the yarn to the primary backing, it mustpenetrate all or substantially all of the bundle wrap. However, theadhesive must not penetrate past the primary hacking into the exposedyarn to any significant degree or the exposed yarn will become stiff andtheresultant carpet will be unacceptable. Prior to the presentinvention, the use of strong adhesive compositions in carpets has beenimpractical.

It would be highly desirable to provide tufted carpets having improvedtuft lock without increasing the stiffness of exposed yarn and toprovide a process for making these carpets which eliminates the highheating requirements of present systems. -In accordance with the presentinvention, there is provided a process for forming tufted carpetsemploying polyurethane-based adhesive composition. The polyurethaneadhesive is a thixotropic composition comprising a polyol having ahydroxyl number less than 100, a polyisocyanate, a filler and a catalystsystem that promotes reaction of the isocyanate and the polyol to form apolyurethane within a short time after mixing. Penetration of thethixotropic composition into the bundle wrap is controlled by regulatingcarefully its initial viscosity, its thixo- .tropicity, its pot life andthe amount of adhesive expan-v sion during reaction so that the bundlewrap is at least saturated with adhesive without significant penetrationthrough the primary backing.

The thixotropic composition is formed by directing a polyol compositionand a polyisocyanate composition separately to a mixing zone. Theresultant composition is applied evenly to the underside of the primarybacking before a significant degree of curing or blowing is effected.The composition is applied so that the resultant shear forces on thecomposition will reduce its viscosity sufiiciently to promote spreading.The use of a doctor knife is particularly effective for the application.Reaction between the polyisocyanate and water or polyol is initiatedwhen the reactants are mixed so that reaction occurs both prior to andafter the composition passes under the doctor knife. After passing theknife, the composition again becomes thixotropic so that migration intothe yarns on the upper side of the primary backing is prevented. Thewater in the composition causes controlled foaming which improvesadhesive migration into the bundle wrap before the composition is curedand reduces the amount of composition needed to attain desired adhesion.After the'secondary backing, polyurethane composition and primarybacking have been contacted under pressure, the semi-cured polyurethanecomposition is crushed between two rollers, one contacting the exposedyarn and the other contacting the secondary backing so that any cellsformed in the polyurethane are crushed thereby greatly reducing theconcentration of cells in the final polyurethane composition. Thesubsequent crushing of substantially all foam produced prior to finalcuring is essential since the presence of the cells in the finaladhesive will greatly reduce the tuft lock of the final carpet.

The thixotropic composition must have an initial Brookfield viscositybetween about 30,000 and about 100,000 cps. as measured on a BrookfieldViscometer, #7 spindle, to prevent migration thereof into the exposedyarn while permitting it to be spread by means of a doctor knife. Theviscosity measurement is made on the composition not containing catalystto eliminate the effects of curing. The Brookfield Viscometer and itsoperation is described in Development of Research Technique forEvaluating the Low Temperature Fluidity of Automatic TransmissionFluids, published by Coordinating Research Council, Inc., publishedFebruary 1963, appendix A and designated as CRC L-45-1262. It has beenfound that migration cannot be prevented merely by increasing theviscosity of the composition but that it is necessary that thecomposition be thixotropic. In order to attain these characteristics, itis essential that the polyol employed have a hydroxyl number less than100 preferably less than 50. As is well known in the art, the hydroxylnumber is defined as the number of milligrams of potassium hydroxiderequired for the complete neutralization of the hydrolysis product ofthe fully acetylated derivative prepared from one gram of polyetherpolyol. The hydroxyl number can also be defined by the equation:

OH MW wherein OH=hydroxy number of the polyol f=average functionality,i.e., the average number of hydroxyl groups per molecule of a polyol.

MW=average molecular Weight of the polyol It is necessary that thepolyol react and have a low hydroxyl number to reduce the concentrationof diisocyanate needed to effect complete reaction of the polyol to thepolyurethane. When employing liquid diisocyanates, increased amounts ofdiisocyanate will reduce the viscosity of the resultant compositionbelow that desired to pre vent migration of the composition into theexposed yarn. On the other hand, when a solid diisocyanate reactant isemployed, excessive amounts will cause the resultant composition to bepaste-like rendering it very difiicult to spread. Accordingly, while lowmolecular weight polyols can be employed withsolid diisocyanates andhigh molecular weight polyols can be employed with liquid diisocyanates,in each case the hydroxyl number of the polyol must be low to attainproper physical characteristics of the resultant composition.Accordingly, when employing solid diisocyanate reactants, the polyolshould have a molecular weight between about 1000 and about 3000 toattain the proper viscosity characteristics of the resultantcomposition. On the other hand, when the liquid diisocyanate reactant isemployed, the polyol should have a molecular weight of between about3000 and about 9000 to attain the desired viscosity characteristics ofthe resultant composition.

In one aspect of the present invention, a polyurethane prepolymer can beemployed to replace or to be mixed with the polyol in the composition.These prepolymers are prepared by means well known in the art, i.e., byincomplete reaction of a polyol with a diisocyanate. The molecuar weightof the prepolymer and the type of diisocyanate are chosen with theconsiderations described above in mind.

While careful selection of the polyol or prepolymer and the diisocyanateprovide a means for controlling the viscosity of the resulantcomposition, the composition cannot be made thixotropic to the desireddegree by controlling the relative concentrations of only these tworeactants. A suitable filler must be added in amounts sufficient torender the overall composition thixotropic to the desired degree butless than that which will cause the composition to become paste-like.The concentration of filler is dependent upon the type of filleremployed since the degree of thixotropicity varies with the filler used.Generally, the filler, is employed in amounts of between 15 and about300 per parts of polyol or prepolymer reacant. Representative suitablefillers include asbestos, zinc oxide, clay, feldspar or the like, ormixtures thereof. Fillers such as silica, or calcium carbonate alone arenot desirable since high concentrations are needed to attain the desiredlevel of thixotropicity, but can be mixed with the suitable fillers. Itis preferred to employ asbestos powder as the filler either alone or inconjunction with other fillers as satisfactory thixotropiccharacteristics and reduced flamability of the composition are achievedtherewith.

The type of catalyst system employed in the thixotropic composition issuch as to regulate the pot life i.e., the time for 100% viscosityincrease, thereof to between about 10 and about 60 seconds at moderatetemperatures up to about 23 C. after mixing the reactants so that theadhesive comopsition cures at a rate to permit even application,controlled foaming and foam crushing prior to final cure. It isnecessary to employ a composition that cures quickly, otherwise even thethixtropic composition will penetrate through the primary backing intothe exposed yarn prior to curing. Furthermore, it is not possible toemploy compositions that cure at room temperature only at slow ormoderate rates since the heat requirements to increase the rate of curewill cause a viscosity reduction that overcomes increase in viscositydue to curing thereby resulting in a net viscosity reduction andexcessive penetration past the primary backing. After application of theadhesive, and prior to curing, the temperature should be maintainedbelow that which causes adhesive penetration through the primarybacking. Temperatures between 100 and C. are particularly effective. Thedesired blowing is effected by controlling both the catalyst system andthe water concentration in the thixotropic composition. Generally, wateris present in the thixotropic composition between .01 and .75 parts perhundred parts of polyol reactant, over and above the water normallypresent as absorbed on the filler. The catalyst system not only musteffect rapid curing but also must control formation of carbon dioxideresulting from the reaction of water and diisocyanate. Blowing must becontrolled to effect adhesive expansion between about 100 and 400%,preferably between about 200 to 300% so that the bundle wrap issaturated with adhesive and the adhesive can be crushed subsequently todestroy substantially all of the foam cells prior to final curing.Suitable catalysts are those which do not promote the blowing reactionin preference to the polyurethane reaction and promote the urethaneformation reaction at high rates and are well known in the art such asdibutyl tin dilaurate, stannous octoate, nickel acetyl acetonate, ferricacetyl acetonate and the like.

Suitable polyols which can be employed are the polyether polyols havingan average molecular weight between about 1000 and 9000, preferablybetween 4000 and 8000 and having a hydroxyl number less than 100including polybutylene ether glycol, polyethylene ether glycol,polypropylene ether glycol, 1,2-polydimethylene ether glycol,polydecamethylene ether glycol or polyurethane prepolymers obtained byincompletely reacting a polyol with a diisocyanate, and mixturesthereof. Particularly suitable polyol compositions are those having anaverage molecular weight of between about 6000 and about 7000. Thesepolyethers have a functionality of at least 2.

A variety of polyisocyanates may be reacted with these polyols to obtainsatisfactory polyurethane adhesives. Particularly suitablepolyisocyanates are the aromatic diisocyanates as they are more reactiveand less toxic than the aliphatic diisocyanates. Such diisocyanatesinclude 2,4- tolylene diisocyanate, 2,6-tolylene diisocyanate,naphthylene' 1,4-diisocyanate, and diphenylmethane-4,4'-diisocyanate,3,3'-dimethoxy biphenylene diisocyanate, 4,4-diphenylene diisocyanateand mixtures thereof. The diisothe polyol and with the water present.

The process of this invention can be employed to form a carpet having aprimary and secondary backing and the piling yarn normally employed incarpets including nylon polyamides, rayon, polyesters, wool andacrylics.

This invention will be more fully described with reference to theaccompanying drawing. A tufted primary backing is stored on roller 1 anda secondary backing is stored on roller 2. The tufted primary backing isunrolled from roller 1, passed over guide roll 3 and into 1 box 4wherein itis stored. The primary backing is passed over guide rollers 5,6, 7 and 8 and over adhesive applicator backup roller 9. Simultaneously,the secondary backing is unrolled from roller 2, passed over overheadrollers 12 onto adhesive applicator backup roller 9. The polyolcomposition and isocyanate are dispensed from mixing nozzle 13 onto theunderside of the primary backing. The composition is spread and thesecondary backing is applied to the primary backing by passing thesecondary backing under the doctor blade 14 with the polyol-isocyanatecomposition sandwiched between the secondary backing and the primarybacking. The resulting laminate 15 is passed between pressure rollers 16into oven 17 provided with infrared heaters "18. Substantially, all ofthe polyurethane foam is crushed between rollers 16a. The heatedlaminate is passed out of the oven 17 over turn rolers 19 and 20 intocontact with dryer rollers 21 which may be heated with, for example,steam. The heated laminate is passed over overhead rollers 22, through anap sensor and trimmer assembly 23 onto a finished carpet storage roll24.

The following examples illustrate the present invention and are notintended to limit the same.

EXAMPLE I To a mixing head apparatus adapted to spread a mixture onto amoving carpet are separately charged (1) a. polyol compositioncomprising 100.0 pounds of a polypropylene oxide glycol having ahydroxyl number of about 25, 0.50 pounds of water, 15.0 pounds ofasbestos having an average particle size of about -50 microns, 100.0pounds of calcium carbonate having an average particle size of about 50-150 microns and 0.06 pound of a catalyst comprising di-butyl tindilaurate and (2) a modified diphenylmethane-4,4 diisocyanate. Theresultant mixture has a viscosity (in the absence of catalyst) of about88,000 when measured on a Brookfield Viscometer with spindle No. 7, l0r.p.m., RVF. The resultant mixture was metered onto the underside of aprimary backing through which nylon yarn had been tufted by means of adoctor knife around which the secondary backing was applied, so that theadhesive was applied in an amount of about 18.0 ounces per square yard.After passing the doctor knife, the adhesive was subjected to a gasflame to elevate the temperature to about 135 C.

Both prior to and after passing the doctor knife, the thixotropiccomposition reacted to form a foamed polyurethane composition. After thesecondary backing had been applied, the resulting laminate was passedbetween two rollers to subject the adhesive to the pressure of about 4p.s.i. thereby crushing substantially all of the cells formed in theadhesive. The resulting laminate was passed under heat source and over aseries of heated rolls maintained at about 135 C. and then rolled on astorage roller. About 90 seconds was required between adhesiveapplication and storage.

The resulting laminated carpet was then tested for strength by thedelamination, bundle wrap and tuft lock tests. The carpet was found tohave a tuft lock of about 25 pounds. The bundle wrap was found to beabout 100 percent saturated with polyurethane adhesive and there was nomigration of the polyurethane past the primary backing. EXAMPLE II Thisexample illustrates the use of a polyurethaneforming composition in aprocess which is ineffective for adhering a secondary backing to atufted primary backing.

The following formulation was prepared and mixed.

Materials: Parts by weight 6500 M.W. polypropylene oxide glycol, OH

#25 I 100.00 Water 0.50 Calcium carbonate -i. 100.00 Dibutyltindilaurate .09 Diisocyanate (NCO. Eq. 143) 27.0

The mixture had a viscosity of approximately 20,000, spindle No. 7, 10r.p.m.,. RVF. Thirty seconds reaction time was allowed prior to mixingand before application to a primary backing tufted with nylon yarn,after which a puddle of the mixture was applied to 12" x 12".sample ofunderside of the primary backing. The mixture was doctored or spreadwith a knife edge to a level of approximately 18 ounces per square yard.A similar size sample of woven jute was pressed against the surface androlled with a heavy metal roll. The sample was placed in a lab aircirculating oven for three minutes at 270 F.

After the three-minute cure, the sample was observed and found to haveexcessively deep penetration of the mixture into the fabric. Also, themixture had penetrated into the jute and very little adhesive wasretained between the backings, thereby producing a poorly bonded sampleof jute to the carpet. No asbestos was present in this sample and theviscosity was low, not thixotropic and very temperature unstable(thinned as temperature increased).

EXAMPLE III This example illustrates that a thixotropicpolyurethane-forming composition will effect unsatisfactory adhesionunder processing conditions differing from this invention. The followingformulation was prepared and mixed.

The resulting mixture had a viscosity of approximately 100,000, No. 7spindle, 10 r.p.m., RVF. This mixture was given approximately 30 secondsafter mixing and prior to application and was spread with knife edge toa level of approximately 18 ounces per square yard. A similar sizesample of woven jute was pressed to the adhesive surface and rolled inplace by means of a heavy metal roll and the resultant composite wasplaced in an air circulating oven for approximately ten minutes at 270F.

When the sample was removed from the oven, it was found that excessivepenetration of the adhesive into the jute and carpet had taken place,very little adhesive was found between the carpet and jute and thelamination was poor.

The increase in temeprature of the adhesive caused a severe drop inviscosity, a drop which greatly exceeded the viscosity build-up causedby the reaction.

7 EXAMPLE IV This example illustrates the unsatisfactory resultsobtained when using a polyol with a hydroxyl number above 100. Thefollowing formulation was prepared and mixed.

Material: Parts by weight 425 M.W. polypropylene oxide glycol, OH #270100.00 Water 0.50 Dibutyltin dilaurate 0.06 Calcium carbonate 100.00

Asbestos 15.00 Diisocyanate 80.00

The resultant mixture had a relatively low viscosity, approximately22,000, No. 4, at 10 r.p.m. A 30-second period was elapsed betweenmixing and applying said material. As the material was applied to thecarpet by knife edge it was observed that the adhesive was beingabsorbed into the carpet. Jute was applied to the adhesive and rolled inplace. The sample was placed in an air circulating oven forapproximately 4 minutes at 270 F. When cured the sample was examined andfound the adhesive had penetrated into the yarn and into the jute andthere was very little adhesion of jute to carpet.

I claim:

1. The process of producing carpeting which comprises applying to theunderside of a pile-faced primary backing a thixotropic polyurethanecomposition having an initial viscosity of between 30,000 and 100,000 asmeasured on spindle No. 7, 10 r.p.m., RVF of a Brookfield Viscometer andhaving a pot life of between about 1 and about 60 seconds comprising apolyol having a hydroxyl number less than and a functionality of atleast 2, a diisocyanate, suflicient water to effect between 100 and 400percent expansion of the thixotropic composition during reaction of thepolyol and the diisocyanate, a catalyst to effect reaction of thediisocyanate with the water and the polyol and sufiicient filler torender the composition thixotropic, shearing said composition on saidprimary backing to reduce the viscosity of the composition whileapplying the composition to the primary backing, applying a secondarybacking to the composition after or as said composition has beensheared, crushing substantially all of the cells formed in thecomposition, and curing said composition.

2. The process of claim 1 wherein the filler is asbestos.

3. The process of claim 1 wherein the polyurethane adhesive is expandedto between 200 and 300 percent.

4. The process of claim 1 wherein the laminate is heated to about 100 toC. after applying the secondary backing.

References Cited UNITED STATES PATENTS 3,046,177 7/1962 Hankins 264473,219,502 11/1965 Willy 159-79 3,513,046 5/1970 Westfield 156--723,519,526 7/1970 Carey et a1 156-79 X WILLIAM A. POWELL, PrimaryExaminer US. Cl. X.R.

Patent No. 3 70 5 v I Dated o 25 1 912 Inventofls) Clalide Edward TerryIt is Certified thaterror appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

(l 0111mm line 41 delete "'war'p"" aridadd- =-w ra'p 1 Columfi .4, line6 insert "about" before -15 Colutnn line 32; d'eie te w "1" god add -.10;- I l Signed and sealed this 8th day: of May 1973- firemen"BLFETCHERQR.' 1 Attesting: Officer 1v. 1 t v I I Commissioner of- Patents

